Yes, this is passive, and this phrase is certainly used often in office environments. The reason for the passive voice can be to convey that in fact, nobody will read this message - neither the recipient nor their secretaries, deputies, family members or the like. Writing this in active voice ("Niemand wird Ihre Mitteilung lesen.") would sound downright rude.

So by using the passive voice, the sender is able to politely concentrate on the message not being read by anyone, instead of directly specifying the parties who will not read that message (thereby possibly implying there will be somebody else who will read it anyway).